Or HaChaim on Numbers 11:17/אור החיים על במדבר י״א:י״ז

1 ואצלתי מן הרוח, "and I will hold back from the spirit, etc." The manner in which the Torah describes the transfer of part of Moses' Holy Spirit to the elders was meant to emphasise that Moses had possessed sufficient Holy Spirit to cope with the task allocated to Him by G'd. G'd did not need to increase the total amount of Holy Spirit available for that task. He simply reduced the amount of Holy Spirit which Moses had enjoyed up until that time.

2ולא תשא אתה לבדך, "so that you will not bear it alone." In this verse G'd precluded Moses from retracting on his complaint and expressing willingness to carry on as before. The words לא תשא are equivalent to G'd saying: "you will no longer carry the burden alone under any circumstances." The verse also hints that henceforth Moses' exalted position of authority would no longer be exclusive, and that he would have to share his authority. This is a secondary meaning of the word תשא, i.e. "you will no longer be the only one who has been elevated to high stature." I have come across the following remarks in Bamidbar Rabbah 15: "G'd said to Moses I have equipped you with sufficient insight and knowledge to be a provider for My children and you have been the only one equipped with such stature. From now on they will take from what is yours." According to the scholars who have said in Sanhedrin 17 that the words ולא יספו (11,25) mean that Eldod and Medod did not stop prophesying the words לא תשא may refer to a prophecy such as the word משא in Maleachi 1,1. Accordingly G'd told Moses that henceforth he would no longer be the only prophet in Israel but would have to share that distinction with the elders.